Transition from Vortical to Alfvenic-like Fermi Electron Acceleration in Magnetic Reconnection with Increasing Guide Field

Using particle-in-cell simulations of magnetic reconnection (MR), we investigate how the changing magnetic guide field strength impacts the evolution of electron Kelvin-Helmholtz instability (EKHI) and the associated Fermi electron acceleration proposed by H. Che & G. P. Zank. Through this investigation, an Alfvenic-like Fermi electron acceleration mechanism is discovered for strong guide field MR B-g/B-0 > 2.5, where B-g is the magnetic guide field. The electrons are accelerated by the intensive electric potential produced through delta U(i)xB , where the ion velocity fluctuations delta U-i propagate parallel to the direction of the Alfven-like waves. Differing from the two-stage second-order Fermi acceleration produced by the stochastic electric field of EKHI, the Alfv & eacute;n-like wave mechanism is a much more efficient one-stage process that produces a much harder power-law electron energy spectrum, with an index similar to 2, than that of the EKHI, with an index similar to 4.